Operations is the star of the Sanitation Districts of Los Angeles County (SDLAC). From out-of-the-box ideas to improve treatment plant performance to quick thinking in emergencies, the operations team has played a leading role in the districts’ success.
“I’m endlessly impressed with our operations group,” says Vicki Conway, head of the Wastewater Management Department. “They’re on the job protecting public health and safety, 24-7.”
The districts are a regional agency consisting of 24 independent special districts, providing wastewater and solid waste management to about 5.3 million people in Los Angeles County. The service area covers about 820 square miles and encompasses 78 cities and unincorporated territory within the county.
The districts convey and treat some 480 mgd, of which 170 mgd is available, after a high level of treatment, for reuse in the dry Southern California climate. The 24 districts work cooperatively with one administrative staff, led by Steve Maguin, the chief engineer and general manager.
Home-grown solutions
As the districts faced the probability of stricter effluent requirements (more restrictive than state and federal drinking water standards) at the Valencia Water Reclamation Facility (21.6 design mgd), supervisors, operators, and research and development specialists brought their decades of experience to bear and developed a home-grown solution.
It promises to enable the Valencia plant to meet tightening nitrogen removal requirements with existing treatment processes. That’s critical, because the plant has no room for additional treatment facilities.
“The original plant consisted of two three-pass conventional step-feed activated sludge systems for carbonaceous BOD removal,” says Ron Kettle, desert facilities superintendent. “In 1994, the Los Angeles Regional Water Quality Control Board mandated more stringent standards for inorganic nitrogen in the Santa Clara River, our receiving stream. So we converted the two step-feed systems to the Modified Ludzack-Ettinger process (MLE) and built three additional two-pass MLE units.”
The districts’ research staff also developed an innovative process to treat a filtrate sidestream, which was high in ammonia nitrogen, from the dewatering of anaerobically digested biosolids. This innovative process combines the filtrate and return activated sludge in an aerated tank, which converts all of the ammonia, thus lessening the load on the aeration units. It also seeds the secondary aeration units with nitrifying bacteria.
The MLE process features a recycle line that enables a 100 to 300 percent internal recycle of mixed liquor from the end of the biological treatment process to the front of the individual units. “Since then, we’ve comfortably met the interim effluent limit of 10 mg/L for NO3-N plus NO2-N,” Kettle reports.
Never stay the same
But in 2003, the water board adopted a nitrogen total maximum daily load (TMDL) for the Santa Clara River to address nitrogen impairments. The TMDL included waste load allocations (new effluent limits) for the Valencia plant for ammonia, nitrate and nitrite. Since compliance with the new nitrogen limits required additional treatment, the water board provided interim effluent limits to the plant until the necessary treatment modification could be made to meet the final effluent limits.
In March 2009, the interim limits will be replaced by new final limits of 6.8 mg/l for NO3-N plus NO2-N and 1.75 mg/l for NH3-N, on a monthly average basis. “This will present us with a significant challenge,” Kettle says. “As flows continue to increase, and hydraulic residence time decreases, we do not want to exceed the nitrogen limits.”
The issue could be even more serious during cold weather, explains Chi-Chung Tang, of the SDLAC’s research staff. “We were occasionally bumping up against the final effluent limits, especially in the winter,” he says. “Without further modifications to the biological process, it is unlikely that the plant could consistently comply with the future final effluent limits.”
Conversion to testing
Enter the SDLAC operation and research team’s ingenuity. Using the original three-pass treatment units and the additional MLE units, the team decided to turn the Valencia plant into a full-scale testing facility.
“The channels and appurtenances of the old step-feed system were still in place,” explains Kettle, “so we were able to run one train as a step-feed system for nitrification, and another as the MLE process. In the third, we created a hybrid process, and then ran all three side-by-side and tracked results.”
The hybrid process is a unit run in step feed mode with internal mixed liquor recycle. Plant operations supervisor Greg Osburne describes some of the innovative thinking that led to the improved performance.
“One of the things that popped into our heads was to rethink where we were bringing the primary effluent into the system,” he says. Originally, the stream entered as a plug flow into the selector zone, but the operations team felt they might get better denitrification if they spread the carbon source around.
“Using step feed gates allows some of the primary effluent to be fed further into the unit, and that has led to better contact and improved denitrification,” Osburne says. The team also looked at aeration and mixing, and made adjustments that are paying off.
Immediate improvement
“The existing system had a deep floating mixer and a shallow floating mixer,” says Osburne. “In the hybrid system, we’re now using a submersible mixer with the deep floating mixer in order to enhance mixing and achieve better denitrification.” They’ve also replaced the bubbling aerator with a floating mixer in the anoxic zone, since adding oxygen there was defeating the purpose of the denitrification process.
The filtrate from biosolids handling, high in ammonia, got their attention, as well. “The filtrate contains as much as 1,000 parts of ammonia,” Osburne says. Using existing tankage for filtrate storage, they’ve been able to spread out the flow and loading, and that has helped the nitrogen removal process.
Improved performance was evident right from the start, according to Kettle. “Right away, we saw better nitrogen numbers, and the system looked better,” he says. “We could see improved appearance, especially in the sedimentation tanks.”
Longer-term results compiled over the period have unquestionably demonstrated that the hybrid system is superior in removing nitrogen. “In full-scale testing, the hybrid configuration produced an effluent that contained less NO3-N plus NO2-N than the step feed or MLE configuration,” Kettle, Osburne, and other authors reported in a WEFTEC paper. Levels are typically lower by 2 mg/l throughout the day.
They concluded that conversion of three of the MLE units to the hybrid design proved very beneficial and are planning on converting the two remaining units. That should be adequate to meet the future nitrogen effluent limits.
Quick thinking
Staff ingenuity also comes into play in more immediate ways. In two instances, quick thinking by Kettle, Osburne, Michael Creel, and Pat Dial has prevented discharge violations at the Valencia and San Jose Creek East water reclamation plants.
“At Valencia, one of the transformers feeding utility power to the plant failed, leaving about half the plant without electricity,” recalls operations section head Dave Snyder. “The generator we had on hand failed to start, as well. It was late on a Saturday evening, and flows into the plant were still pretty elevated.”
Operators pushed as much flow through the functioning part of the plant as they could and, realizing that flows would drop off within the next two hours, diverted any excess to their flow equalization tank on site. “This bought us time to get a temporary generator in place,” Snyder says. “Without the equalization tank, we wouldn’t have been able to get through the emergency,” says Snyder.
At San Jose Creek East, the issue was more complicated. During a scheduled replacement of an electrical transformer that fed a portion of the plant, a temporary generator quit working and would not restart. The distributive control system (DCS) was down, and so were the primary chlorination and dechlorination systems. “We were essentially flying blind for a few hours,” says Snyder.
Since San Jose Creek East operates in conjunction with six other plants and tributary trunk sewers as part of a larger Joint Outfall System in Los Angeles County, the San Jose Creek staff, led by Creel and Dial, were able to divert some flow to the San Jose Creek West plant and use excess capacity in a bypass sewer line to accommodate most of the remaining flow.
Fast change-out
This limited the flow that had to be treated at the east plant and greatly lengthened the time before the un-chlorinated slug of flow entering the chlorine contact tanks would exit the plant. As un-chlorinated flow entered these tanks, it continued to push the previously chlorinated effluent through and out of the tanks. A backup sodium bisulfite system designed to dose automatically upon loss of power, maintained dechlorination while the primary dechlorination system was out of commission.
With the operation stabilized, electrical crews expedited the change-out of the transformer and all systems, were back in business. Once the DCS was up and running, “operators could track the wave of unchlorinated effluent moving through the contact tanks,” Snyder says.
As the chlorine residual began to drop, indicating that the wave was beginning to exit the plant, operators strategically diverted the slug of unchlorinated effluent to the bypass sewer. To ensure adequate bypass capacity in the sewer, they redirected the influent sewage, which they were previously bypassing, back into the head end of the plant. Once the slug of unchlorinated effluent was completely bypassed, the plant returned to nominal operation.
“Quick-thinking operators who know the options available to them and can adapt — that’s the key to solving those emergencies that are bound to happen in wastewater treatment,” Snyder says.
Down with bureaucracy
The Sanitation Districts of Los Angeles County is a huge entity, and it’s sometimes true that large organizations suffer from bureaucracy and a tendency toward the status quo. Not so here.
“For the 35 years that I have worked for the districts, we’ve built capacity and capability ourselves,” explains Kettle. “The districts are known for forward thinking. Our departments work well together, and with the increasingly restrictive effluent limits for river discharge, we are constantly being challenged.”
Osburne and Tang agree. They report that the research staff gets out in the field, works with the department and section heads, operations and maintenance, and the districts’ design team to develop hands-on information that helps make the plant better.
“There’s a lot of back and forth. It’s not just top-down,” says Osburne. “We’re always looking for ways to make things run better. That means less headaches for us.”
